The discovery of an unusual specimen of Psorophora in Mississippi led to a search for new diagnostic characters on the seven United States species of Psorophora (Janthinosoma): Psorophora cyanescens, Ps. ferox, Ps. horrida, Ps. johnstonii, Ps. longipalpus, Ps. mathesoni, and Ps. mexicana. New characters were found and diagnostic descriptions and a new key are provided for identifying female specimens. The new key stresses morphological differences other than color patterns on the hindtarsi, however, notes on hindtarsal color and other variations found on each species are also provided. The status of Ps. mexicana specimens recorded from Texas is reviewed and a list of collections of this species since the 1945 record in Texas is provided. Evidence is provided supporting the recognition of Ps. mexicana as a distinct species.